An electric double layer capacitor is expected to withstand a high voltage. A conventional method of preparing electrolyte synthetically is to produce electrolyte by combining numbers of conceivable solutes and solvents in order to obtain a higher withstanding voltage. The withstanding voltage of the electrolyte produced is measured to examine whether or not it meets the target withstanding voltage. Such a process of trial and error is repeated for preparing electrolyte, and then an amount of positive and negative electrodes is adjusted in order to make a full use of the withstanding voltage of the electrolyte thus prepared. Electric double layer capacitors have been thus manufactured.
The foregoing conventional method has a problem of taking an extremely long time to develop electrolyte. To be more specific, it needs the following three steps: (1) select appropriate solutes and solvents from among numbers of conceivable ones; (2) prepare electrolyte synthetically by dissolving the solutes into the solvents selected; and (3) measure a withstanding voltage of the electrolyte. Those steps are repeated again and again to obtain a target electrolyte. Therefore, it takes an extremely long time to complete the target electrolyte. As a result, the foregoing problem has caused delay in developing electric double layer capacitors.